The word(s) "observe" appears 13 time(s) in 12 verse(s) in Quran in Mohsin Khan translation.

(1) The month of Ramadan in which was revealed the Qur'an, a guidance for mankind and clear proofs for the guidance and the criterion (between right and wrong). So whoever of you sights (the crescent on the first night of) the month (of Ramadan i.e. is present at his home), he must observe Saum (fasts) that month, and whoever is ill or on a journey, the same number [of days which one did not observe Saum (fasts) must be made up] from other days. Allah intends for you ease, and He does not want to make things difficult for you. (He wants that you) must complete the same number (of days), and that you must magnify Allah [i.e. to say Takbir (Allahu Akbar; Allah is the Most Great] for having guided you so that you may be grateful to Him.

(2) And perform properly (i.e. all the ceremonies according to the ways of Prophet Muhammad صلى الله عليه وسلم), the Hajj and 'Umrah (i.e. the pilgrimage to Makkah) for Allah. But if you are prevented (from completing them), sacrifice a Hady (animal, i.e. a sheep, a cow, or a camel) such as you can afford, and do not shave your heads until the Hady reaches the place of sacrifice. And whosoever of you is ill or has an ailment in his scalp (necessitating shaving), he must pay a Fidyah (ransom) of either observing Saum (fasts) (three days) or giving Sadaqah (charity - feeding six poor persons) or offering sacrifice (one sheep). Then if you are in safety and whosoever performs the 'Umrah in the months of Hajj before (performing) the Hajj, (i.e. Hajj-at-Tamattu' and Al-Qiran), he must slaughter a Hady such as he can afford, but if he cannot afford it, he should observe Saum (fasts) three days during the Hajj and seven days after his return (to his home), making ten days in all. This is for him whose family is not present at Al-Masjid-Al-Haram (i.e. non-resident of Makkah). And fear Allah much and know that Allah is Severe in punishment.

(3) They (the hypocrites) will present their excuses to you (Muslims), when you return to them. Say (O Muhammad صلى الله عليه وسلم) "Present no excuses, we shall not believe you. Allah has already informed us of the news concerning you. Allah and His Messenger will observe your deeds. In the end you will be brought back to the All-Knower of the unseen and the seen, then He (Allah) will inform you of what you used to do." [Tafsir At-Tabari]

(4) (The believers whose lives Allah has purchased are) those who turn to Allah in repentance (from polytheism and hypocrisy, etc.), who worship (Him), who praise (Him), who fast (or go out in Allah's Cause), who bow down (in prayer), who prostrate themselves (in prayer), who enjoin (on people) Al-Ma'ruf (i.e. Islamic Monotheism and all what Islam has ordained) and forbid (people) from Al-Munkar (i.e. disbelief, polytheism of all kinds and all that Islam has forbidden), and who observe the limits set by Allah (do all that Allah has ordained and abstain from all kinds of sins and evil deeds which Allah has forbidden). And give glad tidings to the believers.

(5) Have they not observed things that Allah has created: (how) their shadows incline to the right and to the left, making prostration unto Allah, and they are lowly?

(6) Do they not observe the earth - how much of every good kind We cause to grow therein?

(7) He said: "Do you observe that which you have been worshipping -

(8) Verily, the Muslims (those who submit to Allah in Islam) men and women, the believers men and women (who believe in Islamic Monotheism), the men and the women who are obedient (to Allah), the men and women who are truthful (in their speech and deeds), the men and the women who are patient (in performing all the duties which Allah has ordered and in abstaining from all that Allah has forbidden), the men and the women who are humble (before their Lord - Allah), the men and the women who give Sadaqat (i.e. Zakat, and alms), the men and the women who observe Saum (fast) (the obligatory fasting during the month of Ramadan, and the optional Nawafil fasting), the men and the women who guard their chastity (from illegal sexual acts) and the men and the women who remember Allah much with their hearts and tongues Allah has prepared for them forgiveness and a great reward (i.e. Paradise).

(9) Did you (O Muhammad صلى الله عليه وسلم) observe him who turned away (from Islam).

(10) And observe the weight with equity and do not make the balance deficient.